pe1chl,
I'm afraid that you're misinterpreting the use of reduced blanking as proof that a single link TMDS card can always drive 1600x1200. Running 1600x1200@60 requires at least a 161Hz pixelclock.

I've not come across any GeForce 6200 cards that were capable of driving 1600x1200 without reduced blanking.

That said, I suppose its possible that mbidewel has hardware that is capable of doing 1600x1200 at a refresh rate less than 60Hz, however since a verbose bug report wasn't provided, its not possible to say for certain.